docs: def write(self, source=None, **kwargs):
          '''Wrappe    r to call the writer's write method if present.
  
          Args:
              source(pandasdmx.model.Message, iterable): stuff to be written.
                  If a :class:`pandasdmx.model.Message` is given, the writer
                  itself must determine what to write unless specified in the
                  keyword arguments. If an iterable is given,
                  the writer should write each item. Keyword arguments may
                  specify what to do with the output depending on the writer's API. Defaults to self.msg.
  
          Returns:
              type: anything the writer returns.
          '''
  
          if not source:
              source = self.msg
          return self._writer.write(source=source, **kwargs)